1. Field of the Invention
This invention relates to an automatic piloting device for an aerodyne such as e.g. a helicopter.
The purpose of such devices is generally to unburden the pilot of a certain number of tasks while improving the flight characteristics of the aerodyne which is usually unstable, and while performing certain piloting tasks such as the maintaining of the aerodyne on a certain trajectory selected by the pilot.
The aim of the automatic piloting devices intended to equip helicopters is more particularly to improve the stability of the aircraft during manual piloting, and to provide the pilot with an impression of greater stability and homogeneity as regards the characteristics of the effects of the different flight control surfaces.
2. Description of the Prior Art
Up to now, these devices carried out, for each of the three piloting axes (roll, pitch and yaw), an analog computation enabling controlling of the set of actuators acting on the flight control surfaces as a function of commands from the pilot and the information provided by the sensors.
Generally, the actuators for a piloting axis comprise a low-authority series thrustor with very fast motion, and a trim thrustor with full authority and slower motion, intended to recenter the position of the series thrustor.
In view of the fact that each piloting axis is governed by different automatic control laws, each computation is different. It ensues that the cost of such a device is very high as each computer must be designed, tested and certified individually.
Moreover, helicopters are intended to carry out a large number of missions. In order to be authorized to fly and to carry out these missions under satisfactory safety conditions, a helicopter must be submitted for certification. This certification mainly concerns the safety of the helicopter and third parties it flies over. It deals with the devices susceptible of having an impact on its level of safety, and notably the automatic piloting device.
In view of cost considerations and because the flight characteristics of helicopters can be very different from one model to another, the equipment therein must be adapted to their features and to the missions for which they are intended.
Since the emergence of digital technologies, proposals have been made, with a view to integrating a large number of functions into a system that is less cumbersome, while being open-ended and more easily maintained, to integrate all the functions of the three analog computations of the automatic piloting device into a single digital computer. This solution allows considerable flexibility in adapting the device to each type of utilisation, this adaptation being possible by simply changing the version of the programme piloting the actuators. However, though this solution avoids having to manufacture a computer for each type of aircraft and for each type of mission, it does not dispense with the certification stage for each version.
Furthermore, the computing power required varies significantly depending on whether one or three axes must be controlled simultaneously, and therefore, in order to optimize costs, several hardware configurations of the piloting device must nonetheless be proposed in order to meet the mission requirements in as satisfactory a manner as possible.
Digital computers for automatic piloting are usually comprised of several electronic boards corresponding to the digital heart, power supply, I/O management, and generating of actuator power commands. All these boards communicate with one another via an interconnection board known as a "backpanel" board.
This structure implies that each board be identified separately, prior to integration and identification of the overall computer.
Furthermore, in order to repair a faulty computer, the entire unit must be tested to locate the faulty board. Once it has been repaired or replaced, the latter must be tested separately and then integrated into the overall computer which must be retested for acceptance.
This structure thus leads to relatively complex, and therefore costly, maintenance and acceptance procedures.